1,2

a(n) = ceiling(n*n!/e) - (1-(-1)^n)/2.

E.g.f.: x^2*exp(-x)/(1-x)^2. - Vladeta Jovovic (vladeta(AT)Eunet.yu), Nov 20 2003

a:=n->sum((n+1)!*sum((-1)^k/k!, j=1..n-k), k=0..n): seq(a(n), n=0..18); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jun 03 2007

a:=n->n!*sum((-1)^k/k!, k=0..n): seq(a(n)*n, n=1..19); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 18 2007

with (combstruct):with (combinat):a:=proc(m) [ZL, {ZL=Set(Cycle(Z, card>=m))}, labeled]; end: ZLL:=a(2):seq(count(ZLL, size=n)*fibonacci(2, n), n=1..19); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jun 11 2008

with (combstruct):a:=proc(m) [ZL, {ZL=Set(Cycle(Z, card>=m))}, labeled]; end: ZLL:=a(2):seq(count(ZLL, size=n)*n, n=1..19); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jun 11 2008

Cf. A000246.

Cf. A000274.

Cf. A000166.

Sequence in context: A130874 A019020 A101609 this_sequence A074424 A002868 A002869

Adjacent sequences: A086322 A086323 A086324 this_sequence A086326 A086327 A086328

nonn

Benoit Cloitre (benoit7848c(AT)orange.fr), Aug 30 2003